Device housing a battery and charging pad

ABSTRACT

A device housing a battery ( 50 ) includes a receiving coil ( 51 ), and a charging pad ( 10 ) includes a transmitting coil ( 11 ) that magnetically couples with, and supplies charging power to the receiving coil. The device further includes a modulator circuit ( 61 ) that changes the impedance of the receiving coil according to internal battery data. The charging pad further includes a detection circuit ( 17 ) that detects receiving coil impedance changes to detect the battery data. The modulator circuit has a load circuit ( 62 ) connected in parallel with the receiving coil and has a series-connected switching device ( 64 ) and impedance modulating capacitor ( 63 ), and a control circuit ( 65 ) that switches the load circuit switching device ON and OFF according to the battery data. The modulator circuit switches the switching device ( 64 ) ON and OFF to transmit battery data to the charging pad.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device housing a battery (orbatteries) such as a battery pack or mobile telephone, and to a chargingpad that transmits power by magnetic induction to the device housing abattery to charge the battery inside.

2. Description of the Related Art

A charging pad (charging stand, charging cradle) has been developed tocharge a battery housed in a device by transmitting power from atransmitting coil (power supply coil, primary coil) to a receiving coil(induction coil, secondary coil) by magnetic induction. (Refer toJapanese Laid-Open Patent Publication H09-63655 (1997).)

JP H09-63655A cites a configuration with a charging pad housing atransmitting coil driven by an alternating current (AC) power source,and a battery pack containing a receiving coil that magnetically coupleswith the transmitting coil.

The battery pack houses circuitry to rectify AC power induced in thereceiving coil and supply the rectified power to charge the battery.With this system, a battery pack can be placed on the charging pad tocharge the battery pack battery without direct physical contact.

SUMMARY OF THE INVENTION

In a system as described in JP H09-63655A, which magnetically couples atransmitting coil and receiving coil to transmit battery charging power,it is necessary to transmit the fact that battery charging has beencompleted from the battery-side to the power supply-side to stop thesupply of power to the transmitting coil and terminate battery charging.During battery charging as well, by transmitting battery informationsuch as battery voltage, charging current, and temperature, charging canbe performed under ideal conditions. The receiving coil on thebattery-side can be magnetically excited when battery full-charge isdetected, and the magnetic field resulting from receiving coilexcitation can be detected by a sensor provided on the powersupply-side. This arrangement can transmit battery full-chargeinformation from the battery-side to the battery charging powersupply-side. However, this configuration has the drawbacks that thecircuit structure to transmit battery information from the battery-sideto the power supply-side is complex, and it is difficult to accuratelytransmit rapidly varying battery data in real-time.

The present invention was developed with the object of furthercorrecting the drawbacks described above. Thus, it is an importantobject of the present invention to provide a device housing a batteryand charging pad that can rapidly transmit battery information to thepower supply-side charging pad in real-time while maintaining a simplecircuit structure.

The device housing a battery and charging pad of the present inventionis made up of a device housing a battery 50, 70, 80 provided with areceiving coil 51 that supplies power to charge the internal battery 52,and a charging pad 10 provided with a transmitting coil 11 thatmagnetically couples with, and supplies charging power to the receivingcoil 51 in the device housing a battery 50, 70, 80. The device housing abattery 50, 70, 80 is provided with a modulator circuit 61, 71, 81 thatchanges the impedance of the receiving coil 51 according to internalbattery 52 data. The charging pad 10 is provided with a detectioncircuit 17 that detects battery data via the transmitting coil 11 bydetecting modulator circuit 61, 71, 81 impedance changes in thereceiving coil 51. Further, the modulator circuit 61, 71, 81 is providedwith a load circuit 62, 72, 82 that has a switching device 64, 74, 84connected in series with an impedance modulating capacitor 63 that isconnected in parallel with the receiving coil 51, and a control circuit65, 75, 85 that switches the load circuit 62, 72, 82 switching device64, 74, 84 ON and OFF according to the battery data. The modulatorcircuit 61, 71, 81 switching device 64, 74, 84 is switched ON and OFF totransmit battery data to the charging pad 10.

The device housing a battery and charging pad described above has thecharacteristic that battery information can be rapidly transmitted tothe power supply-side charging pad in real-time while maintaining asimple circuit structure. This is because the device housing a batterymodulator circuit has an impedance modulating capacitor connected to thereceiving coil, and connection of that impedance modulating capacitor isswitched ON and OFF by the switching device to transmit battery data tothe charging pad. For example, if the modulator circuit switching deviceis switched ON and then OFF to connect and then disconnect the impedancemodulating capacitor and the receiving coil, various parameters in thecharging pad transmitting coil change such as transmitting coil voltage,current, phase, and transmission efficiency. The charging pad detectioncircuit can detect any one of those changing parameters to determine thebattery data transmitted from the device housing a battery. Further,since the impedance modulating capacitor is connected to the receivingcoil and the change in transmitted current due to the impedancemodulating capacitor is small, parameter changes can be detected todetermine the battery data while charging the battery.

In the device housing a battery and charging pad of the presentinvention, the detection circuit 17 can detect receiving coil 51impedance changes to detect battery information from either transmittingcoil 11 voltage changes, current level changes, current-voltage phaserelation changes, or transmission efficiency changes. As a result of thecircuit structure, the charging pad can accurately detect connection ordisconnection of the impedance modulating capacitor to the receivingcoil by changes in various transmitting coil parameters.

In the device housing a battery and charging pad of the presentinvention, a series capacitor 55 can be connected in series with thereceiving coil 51. With this circuit structure, battery information canbe transmitted while efficiently transmitting power from thetransmitting coil to the receiving coil for efficient battery charging.This is because for high current transmission, power transmission ismore efficient with a capacitor connected in series with the receivingcoil than with a capacitor connected in parallel. Further, power isnormally transmitted to the receiving coil with a series-connectedcapacitor, and the low capacitance impedance modulating capacitor isonly connected in parallel for extremely short time periods to transmitbattery information.

In the device housing a battery and charging pad of the presentinvention, the battery information transmitted from the device housing abattery 50, 70, 80 to the charging pad 10 can include any one of thefollowing data: voltage of the battery being charged, charging current,battery temperature, serial number, allowable battery charging currentthat determines the charging current, and allowable battery temperaturethat controls battery charging. With this circuit structure, the batterycan be charged under favorable conditions while transmitting variousbattery data from the device housing a battery to the charging pad.

In the device housing a battery and charging pad of the presentinvention, the device housing a battery 50, 70, 80 can be provided witha rectifying circuit 53 to rectify AC induced in the receiving coil 51from the transmitting coil 11, and the load circuit 62, 72, 82 can beconnected to the input-side of that rectifying circuit 53. With thiscircuit structure, receiving coil impedance changes can be stablydetected for accurate battery data detection at the charging padindependent of the rectifying circuit configuration.

In the device housing a battery and charging pad of the presentinvention, the rectifying circuit 53 can be either a synchronousrectifying circuit 53A or a diode-bridge circuit 53B. With this circuitstructure, AC induced in the receiving coil can be efficientlyrectified. Since field-effect transistors (FETs) of a synchronousrectifying circuit switch in phase with the AC power, batteryshort-circuit current flow can be reduced for accurate battery datatransmission. This is because even when FETs that conduct in bothdirections in the ON state connect the impedance modulating capacitor inparallel with the battery, battery short-circuit current flow due to theimpedance modulating capacitor is reduced. Further, with a diode-bridgerectifying circuit, a simple circuit structure can be maintained whilereducing battery short circuit current flow to allow battery datatransmission during charging.

In the device housing a battery and charging pad of the presentinvention, the charging pad 10 can be provided with a case 20 having acharging region where a device housing a battery 50, 70, 80 can beplaced in a removable manner, a moving mechanism 13 that moves thetransmitting coil 11 close to the receiving coil 51, and a positiondetection controller 14, 44 that detects the position of the receivingcoil 51 in a device housing a battery 50, 70, 80 placed in the chargingregion and controls the moving mechanism 13 to move the transmittingcoil 11 close to the receiving coil 51. The position detectioncontroller 14, 44 can be provided with position detection coils 30 fixedto the top plate 21 of the case 20, a detection signal generatingcircuit 31 that supplies position detection signals to the positiondetection coils 30, a receiving circuit 32 that receives echo signalsoutput from the receiving coil 51 to the position detection coils 30resulting from excitation of the receiving coil 51 by position detectionsignals supplied to the position detection coils 30 from the detectionsignal generating circuit 31, and a discrimination circuit 33, 43 thatdetermines receiving coil 51 position from the echo signals received bythe receiving circuit 32. The device housing a battery 50, 70, 80 can beprovided with a rectifying circuit 53 connected to the receiving coil 51to convert AC power induced in the receiving coil 51 to direct current(DC) to supply the internal battery 52 with charging power, and a seriescapacitor 55 connected in series with the receiving coil 51. When theposition detection controller 14, 44 is issuing position detectionsignals, the modulator circuit 61, 71, 81 control circuit 65, 75, 85 canswitch the switching device 64, 74, 84 ON to connect the impedancemodulating capacitor 63 to the receiving coil 51.

With this circuit structure, the impedance modulating capacitor used fortransmitting battery data can serve the dual purpose as the capacitorconnected in parallel with the receiving coil for detecting the positionof the device housing a battery. From a different perspective, thecapacitor provided for accurate detection of the position of the devicehousing a battery can transmit the battery information. Consequently, ina device that connects a capacitor to the receiving coil to detect theposition of the device housing a battery, a special-purpose capacitorfor battery data transmission and a switching device to connect thatcapacitor to the receiving coil are unnecessary, and this system ischaracterized by modulating the switching device according to thebattery data to transmit the battery data to the charging pad.

In the device housing a battery and charging pad of the presentinvention, the load circuit 72 can be provided with a pair ofseries-connected switching devices 74X, and impedance modulatingcapacitors 63 connected in series with each of the two switching devices74X. Further, the connection node of the two switching devices 74X canbe connected to the ground line 78, and the pair of switching devices74X can be controlled ON and OFF simultaneously by the control circuit75. With this circuit structure, the switching devices can be switchedON and OFF to transmit battery information and accurately detectreceiving coil position without a common ground line connection betweenthe receiving coil and the rectifying circuit. This system has thecharacteristic that during battery charging, power efficiency isincreased allowing efficient battery charging.

The above and further objects of the present invention as well as thefeatures thereof will become more apparent from the following detaileddescription to be made in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an oblique view of the charging pad of an embodiment of thepresent invention;

FIG. 2 is an abbreviated oblique view showing the internal structure ofthe charging pad shown in FIG. 1;

FIG. 3 is a horizontal cross-section view showing the internal structureof the charging pad shown in FIG. 1;

FIG. 4 is a lengthwise vertical cross-section view of the charging padshown in FIG. 3

FIG. 5 is a widthwise vertical cross-section view of the charging padshown in FIG. 3

FIG. 6 is a circuit diagram showing the position detection controller ofthe charging pad of an embodiment of the present invention;

FIG. 7 is a block diagram of a device housing a battery and charging padof an embodiment of the present invention;

FIG. 8 is a block diagram showing an example of another device housing abattery;

FIG. 9 is a block diagram showing an example of another device housing abattery;

FIG. 10 is a waveform diagram showing an example of an echo signaloutput from the parallel resonant circuit excited by a positiondetection signal;

FIG. 11 is a graph showing oscillation frequency as a function of therelative positional offset of the transmitting coil and the receivingcoil;

FIG. 12 is a circuit diagram showing the position detection controllerof the charging pad of another embodiment of the present invention; and

FIG. 13 is a schematic and graph showing signal levels (amplitudes) ofecho signals induced in the position detection coils of the positiondetection controller shown in FIG. 12.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

The following describes embodiments of the present invention based onthe figures.

FIGS. 1-7 are schematic and diagrammatic views illustrating thestructure and operating principles of the charging pad 10. As shown inFIGS. 1, 2, and 7, devices housing a battery 50 are placed on thecharging pad 10, and the internal battery 52 is charged utilizingmagnetic induction. A device housing a battery 50 contains a receivingcoil 51 that magnetically couples with the transmitting coil 11, and abattery 52 that is charged by power induced in the receiving coil 51.

The device housing a battery 50 is provided with a modulator circuit 61that changes the impedance of the receiving coil 51 according tointernal battery 52 information. The charging pad 10 is provided with adetection circuit 17 that detects receiving coil 51 impedance changesmade by the modulator circuit 61 to detect battery information via thetransmitting coil 11.

The modulator circuit 61 is provided with a load circuit 62 having aswitching device 64 connected in series with an impedance modulatingcapacitor 63 that is connected in parallel with the receiving coil 51,and a control circuit 65 that switches the load circuit 62 switchingdevice 64 ON and OFF according to the battery information. The controlcircuit 65 switches the switching device 64 ON and OFF to transmitbattery information to the charging pad 10. The control circuit 65controls the switching device 64 with digital signals to transmitbattery information such as the voltage of the battery being charged,charging current, battery temperature, battery serial number, allowablebattery charging current that determines the charging current, andallowable battery temperature that controls battery charging. The devicehousing a battery 50 is provided with a battery data detection circuit59 that detects internal battery 52 information. The battery datadetection circuit 59 detects battery information such as batteryvoltage, charging current, and battery temperature, and inputs it to thecontrol circuit 65. The control circuit 65 repeatedly transmits batteryinformation with a given period. Specifically, a time interval forbattery information transmission and a time interval with notransmission are continually repeated with a given period. This periodis set, for example, from 0.1 sec to 5 sec and preferably from 0.1 secto 1 sec. Since battery voltage, current, and temperature change duringcharging, battery data such as these parameters are repeatedlytransmitted with the period described above. However, battery data suchas the battery serial number, the allowable battery charging currentthat determines the charging current, and the allowable batterytemperature that controls battery charging are transmitted once at thebeginning of charging, and subsequent repeated transmission isunnecessary. The modulator circuit 61 switches the switching device 64ON and OFF with digital signals to modulate the capacitance in parallelwith the receiving coil 51 and transmit battery information inaccordance with the transmission timing. For example, the controlcircuit 65 in the modulator circuit 61 can control the switching device64 ON and OFF at a rate of 1000 bps to transmit the battery information.However, the control circuit 65 can also transmit battery information ata rate from 500 bps to 5000 bps. After battery information istransmitted at 1000 bps during the time interval for transmission,battery data transmission is stopped during the time interval with notransmission and battery charging is performed under normal conditions.During the transmission time interval, the switching device 64 isswitched ON and OFF. Switching connects the impedance modulatingcapacitor 63 to the receiving coil 51 for battery data transmission. Asa result of parallel connection of the impedance modulating capacitor 63to the receiving coil 51, conditions for power transmission from thetransmitting coil 11 to the receiving coil 51 are slightly degraded fromthe design conditions for optimum power transmission efficiency.However, the time interval for data transmission is short compared tothe time interval with no transmission, and during the transmission timeinterval, the time that the impedance modulating capacitor 63 isconnected to the receiving coil 51 is extremely short. Consequently,even though transmission efficiency is degraded by connection of theimpedance modulating capacitor 63 to the receiving coil 51, thisdegradation over the total charging power transmission time is at alevel that can be essentially neglected.

The charging pad 10 detection circuit 17 detects receiving coil 51impedance changes by changes in transmitting coil 11 voltage levels, anddetects battery information from the impedance changes. Since thetransmitting coil 11 is magnetically coupled with the receiving coil 51,transmitting coil 11 voltage levels change when the receiving coil 51impedance changes. Since transmitting coil 11 voltage level changes aresynchronous with switching device 64 ON and OFF switching, switchingdevice 64 ON and OFF switching can be detected by the changes intransmitting coil 11 voltage levels. Since the modulator circuit 61switches the switching device 64 ON and OFF with digital signalsrepresenting the battery data, the discharge circuit 17 can detect thebattery data digital signals by detecting ON and OFF switching of theswitching device 64. Consequently, the detection circuit 17 can detectbattery information such as the voltage of the battery being charged,charging current, and battery temperature from the detected digitalsignals.

However, the detection circuit 17 can also detect battery informationfrom changes in transmitting coil 11 current levels, from the phaserelation between the current and voltage, or from changes in thetransmission efficiency. This is because these parameters change as aresult of changes in the receiving coil 51 impedance.

In the charging pad 10 shown in FIGS. 1 and 2, a device housing abattery 50 is placed on the top plate 21 to charge the internal battery52. As shown in FIG. 3, the charging pad 10 houses systems to put thetransmitting coil 11 in close proximity to the receiving coil 51 in thedevice housing a battery 50 for efficient charging of the internalbattery 52. To detect the position of the receiving coil 51, thecharging pad 10 is provided with a position detection controller 14.

FIG. 7 is a circuit diagram showing the charging pad 10 and the devicehousing a battery 50 that is placed on the charging pad 10. The chargingpad 10 is provided with a position detection controller 14 to detect theposition of the receiving coil 51. FIG. 6 shows a block diagram of theposition detection controller 14. The position detection controller 14is provided with a plurality of position detection coils 30 fixed to theinside of the top plate 21 of the charging pad 10 case 20, a detectionsignal generating circuit 31 that supplies position detection signals tothe position detection coils 30, a receiving circuit 32 that receivesecho signals output from the receiving coil 51 to the position detectioncoils 30 as a result of receiving coil 51 excitation by positiondetection signals supplied to the position detection coils 30 from thedetection signal generating circuit 31, and a discrimination circuit 33that determines receiving coil 51 position from the echo signalsreceived by the receiving circuit 32.

The position detection controller 14 described above detects theposition of the receiving coil in the following manner.

(1) The detection signal generating circuit 31 outputs a pulse detectionsignal to a position detection coil 30.(2) The receiving coil 51 is excited by the position detection coil 30,which is supplied with the pulse detection signal. As shown in FIG. 10,an echo signal is output from the receiving coil 51 to the positiondetection coil 30.(3) The receiving circuit 32 receives the echo signal.(4) Each of the plurality of position detection coils 30 is sequentiallyswitched to output a pulse detection signal and receive an echo signal.(5) The discrimination circuit 33 detects the position of the receivingcoil 51 by detecting the amplitude of the echo signal induced in eachposition detection coil 30. The amplitude of the echo signal in aposition detection coil 30 close to the receiving coil 51 is high, andecho signal amplitude drops off as the position of the receiving coil 51becomes further away from the detection coil 30. Consequently, thediscrimination circuit 33 can determine the receiving coil 51 positionfrom echo signal amplitude. The position detection controller 14 of FIG.6 has position detection coils 30 disposed in the X-axis direction andY-axis direction. The position of the receiving coil 51 in the X-axisdirection is determined by X-axis detection coils 30A, and the positionof the receiving coil 51 in the Y-axis direction is determined by Y-axisdetection coils 30B.

As shown in the circuit diagram of FIG. 7, a parallel resonant circuit57 is formed by connecting the impedance modulating capacitor 63 inparallel with the receiving coil 51, and the position detectioncontroller 14 triggers resonance with a pulse signal causing an echosignal to be generated. However, the impedance modulating capacitor 63connected in parallel with the receiving coil 51 slightly lowers thepower efficiency when the internal battery 52 is charged by powerinduced in the receiving coil 51.

The device housing a battery 50 is provided with a rectifying circuit 53connected to the receiving coil 51 to convert AC power induced in thereceiving coil 51 to DC to supply the battery 52 with charging power, aseries capacitor 55 connected in series with the receiving coil 51 toinput receiving coil 51 AC to the rectifying circuit 53, an impedancemodulating capacitor 63 connected in parallel with the receiving coil51, and a switching device 64 that switches the connection of the seriescapacitor 55, the impedance modulating capacitor 63, and the receivingcoil 51. When the position detection controller 14 is issuing positiondetection signals, the device housing a battery 50 switching device 64connects the impedance modulating capacitor 63 to the receiving coil 51.When power is transmitted from the transmitting coil 11 to the receivingcoil 51, the impedance modulating capacitor 63 is disconnected from thereceiving coil 51, and AC power is output from the receiving coil 51 tothe rectifying circuit 53 through the series capacitor 55.

The device housing a battery 50 and charging pad 10 described above havethe characteristic that while a parallel resonant circuit 57 is normallyconnected for accurate location of the receiving coil 51, the impedancemodulating capacitor 63 is disconnected during battery charging to allowthe internal battery to be charged in a power efficient manner. This isbecause during detection of the receiving coil 51 position, echo signalgeneration depends on connection of the impedance modulating capacitor63 to the receiving coil 51. Further, during internal battery 52charging, power efficient battery charging depends on disconnection ofthe parallel-connected impedance modulating capacitor 63 to allowreceiving coil 51 power to be output to the rectifying circuit 53through the series-connected capacitor. Power efficiency during chargingis improved by a circuit configuration that connects a series capacitor55 to the receiving coil 51 compared to low-current transmissionconfigurations with a capacitor connected in parallel with the receivingcoil. With the configuration described above, coil and battery heatgeneration during charging can be controlled, and the internal batterycan be charged efficiently, rapidly, and safely.

Here, the impedance modulating capacitor 63 connected in parallel withthe receiving coil 51, the switching device 64 that connects theimpedance modulating capacitor 63 to the receiving coil 51, and thecontrol circuit 65 that controls the switching device 64 ON and OFF areprovided, and the switching device 64 is switched ON when the positiondetection controller 14 detects receiving coil 51 position. With adevice housing a battery 50 having this circuit configuration, theimpedance modulating capacitor 63, switching device 64, and controlcircuit 65 provided in conjunction with the position detectioncontroller 14 can also be used to transmit battery information. This isbecause the control circuit 65 can switch the switching device 64 ON andOFF according to battery information in digital signal form to changethe load impedance of the receiving coil 51. Consequently, this devicehousing a battery 50 can transmit battery information without providingspecial-purpose circuitry for battery data transmission. Specifically,the same hardware can be utilized by only changing the software forcontrol circuit 65 ON and OFF switching of the switching device 64. Thesoftware can be stored in memory provided in the control circuit 65. Asa result, this device housing a battery 50 can transmit battery data tothe charging pad 10 under ideal conditions without increasingmanufacturing cost.

The device housing a battery 50, 70, 80 shown in FIGS. 7-9 is providedwith a rectifying circuit 53 connected to the receiving coil 51 thatconverts AC induced in the receiving coil 51 to DC to supply chargingpower to the internal battery 52. The rectifying circuit 53 converts ACinput from the receiving coil 51 to DC and outputs that DC power to acharging control circuit 54 that controls internal battery 52 charging.The rectifying circuit 53 of FIGS. 7 and 9 is a synchronous rectifyingcircuit 53A. The synchronous rectifying circuit 53A is provided withfour FETs connected in a bridge configuration, and a switching circuit53 b that switches each of the FETs ON an OFF. The switching circuit 53b switches the FETs 53 a synchronous with the AC output from thereceiving coil 51 to convert the input AC to DC output. Since FET 53 avoltage drop is less than diode voltage drop, the synchronous rectifyingcircuit 53A has the characteristic that AC can be rectified with reducedpower loss due to voltage drops. However, as shown in FIG. 8, adiode-bridge circuit 53B can also clearly be used in place of thesynchronous rectifying circuit as the rectifying circuit 53. Thecharging control circuit 54 fully charges the internal battery 52 withpower input from the rectifying circuit 53. The charging control circuit54 detects full-charge of the internal battery 52 and stops charging. Acharging control circuit 54 for a lithium ion internal battery 52charges the battery 52 to full-charge by constant voltage-constantcurrent charging. A charging control circuit for a nickel hydrideinternal battery charges the battery to full-charge by constant currentcharging.

The device housing a battery 50, 70, 80 of FIGS. 7-9 is provided withthe series capacitor 55 connected in series with the receiving coil 51to efficiently input receiving coil 51 AC to the rectifying circuit 53,the impedance modulating capacitor 63 connected in parallel with thereceiving coil 51, and the switching device 64, 74, 84 that switchesconnection of the series capacitor 55, the impedance modulatingcapacitor 63, and the receiving coil 51.

When position detection signals are output from the position detectioncontroller 14, the switching device 64, 74, 84 connects the impedancemodulating capacitor 63 to the receiving coil 51. The receiving coil 51and impedance modulating capacitor 63 form a parallel resonant circuit57 that is excited by position detection signals issued from theposition detection controller 14 position detection coils 30 to generateecho signals. Resonance resulting in echo signal generation cannot beachieved by receiving coil 51 connection to a series capacitor 55 alone,and connection of the impedance modulating capacitor 63 is necessary.Therefore, when the device housing a battery 50, 70, 80 is placed on thecharging pad 10 and the position detection controller 14 is determiningthe position of the device housing a battery 50, 70, 80, the switchingdevice 64, 74, 84 connects the impedance modulating capacitor 63 to thereceiving coil 51.

However, a receiving coil 51 connected to an impedance modulatingcapacitor 63 has the drawback that power efficiency is reduced becausethe induced power cannot be efficiently output to the rectifying circuit53. The power efficiency for power transferred from the receiving coil51 to the rectifying circuit 53 is improved with connection of theseries capacitor 55 compared to the parallel impedance modulatingcapacitor 63. Consequently, after the receiving coil 51 position hasbeen detected and the transmitting coil 11 has been moved close to thereceiving coil 51, the switching device 64, 74, 84 connects the seriescapacitor 55 to the receiving coil 51 to output induced power from thereceiving coil 51 to the rectifying circuit 53. Specifically, when thetransmitting coil 11 transmits power to the receiving coil 51, theswitching device 64, 74, 84 disconnects the impedance modulatingcapacitor 63 from the receiving coil 51 to leave the series capacitor 55connected instead. In this configuration, AC induced in the receivingcoil 51 is output to the rectifying circuit 55 through the seriescapacitor 55.

The device housing a battery 50 shown in FIG. 7 is provided with theload circuit 62 made up of the impedance modulating capacitor 63, andthe switching device 64 connected in series with the impedancemodulating capacitor 63. The series-connected impedance modulatingcapacitor 63 and switching device 64 are connected in parallel with thereceiving coil 51. The switching device 64 is a semiconductor switchingdevice such as a FET that is controlled ON and OFF by the controlcircuit 65. When the switching device 64 is in the ON state, theimpedance modulating capacitor 63 is connected in parallel with thereceiving coil 51. When the switching device 64 is in the OFF state, theimpedance modulating capacitor 63 is disconnected from the receivingcoil 51. The series capacitor 55 is connected in series with thereceiving coil 51 and connects the receiving coil 51 to the rectifyingcircuit 53.

The control circuit 65 controls the gate voltage of the FET, which isthe switching device 64, to switch the switching device 64 ON and OFF.When the position of the receiving coil 51 is being detected, thecontrol circuit 65 holds the switching device 64 in the ON state toconnect the impedance modulating capacitor 63 to the receiving coil 51.The receiving coil 51 connected in parallel with the impedancemodulating capacitor 63 outputs a large amplitude echo signal whenexcited by a position detection signal from a position detection coil30. Even with the switching device 64 in the ON state, the seriescapacitor 55 is connected between the receiving coil 51 and therectifying circuit 53. However, with the switching device 64 in the ONstate, the receiving coil 51 is connected in parallel with the impedancemodulating capacitor 63 to establish a parallel resonant circuit 57 thatoutputs a large amplitude echo signal when excited by a positiondetection signal.

After the receiving coil 51 position has been detected and thetransmitting coil 11 has been moved close to the receiving coil 51, thecontrol circuit 65 switches the switching device 64 OFF to disconnectthe impedance modulating capacitor 63 from the receiving coil 51.Specifically, when power is transmitted from the transmitting coil 11 tothe receiving coil 51, the control circuit 65 holds the switching device64 in the OFF state to disconnect the impedance modulating capacitor 63from the receiving coil 51. In this configuration, AC power induced inthe receiving coil 51 is efficiently output to the rectifying circuit 53through the series capacitor 55.

The switching device 74 of FIG. 8 is provided with a pair of switchingdevices 74X that are connected in series. The two switching devices 74Xof the figure are semiconductor switching devices such as FETs. The pairof FETs 74 a, 74 b have their sources connected together to connect thedevices in series. In addition, the connection node of the pair ofswitching devices 74X, which is the sources of the two FETs, isconnected to the ground line 78 through a high resistance resistor 79(for example, 100KΩ) to put the connection node essentially at groundpotential. An impedance modulating capacitor 63 is connected in serieswith each of the two switching devices 74X. Each of the FETs 74 a, 74 b,which are the pair of switching devices 74X, is connected to an end ofthe receiving coil 51 through a drain-connected impedance modulatingcapacitor 63. The switching device 74 of this figure connects theseries-connection of an impedance modulating capacitor 63, FET 74 a, FET74 b, and another impedance modulating capacitor 63 in parallel with thereceiving coil 51.

The series capacitor 55 can be connected on the rectifying circuit 53side of the impedance modulating capacitor 63 as shown by the solidlines of the figure, or as shown by the broken lines, it can also beconnected between the impedance modulating capacitor 63 and thereceiving coil 51. A series capacitor 55 connected between the impedancemodulating capacitor 63 and the receiving coil 51 is connected in serieswith the impedance modulating capacitor 63 when the switching devices74X are in the ON state. Consequently, the total capacitance connectedto the receiving coil 51 to form the parallel resonant circuit 57 isequivalent to the series combination of the series capacitor 55 and thetwo impedance modulating capacitors 63.

The two FETs 74 a, 74 b of the pair of switching devices 74X areswitched ON and OFF together by the control circuit 75. The controlcircuit 75 controls the gate voltages of both FETs in the same manner tosimultaneously switch the pair of switching devices 74X ON and OFF. Thecontrol circuit 75 connects the impedance modulating capacitors 63 inparallel with the receiving coil 51 by switching the pair of FETswitching devices 74X to the ON state. When the control circuit 75switches the pair of switching devices 74X to the OFF state, theimpedance modulating capacitors 63 are disconnected from the receivingcoil 51.

When the position of the receiving coil 51 is being detected, thecontrol circuit 75 described above holds the pair of switching devices74X in the ON state to connect the impedance modulating capacitors 63 tothe receiving coil 51. The receiving coil 51 connected in parallel withthe impedance modulating capacitors 63 outputs an echo signal whenexcited into parallel resonance by a position detection signal from aposition detection coil 30.

After the receiving coil 51 position has been detected and thetransmitting coil 11 has been moved close to the receiving coil 51, thecontrol circuit 75 switches the pair of switching devices 74X OFF todisconnect the impedance modulating capacitors 63 from the receivingcoil 51. Specifically, when power is transmitted from the transmittingcoil 11 to the receiving coil 51, the control circuit 75 holds the pairof switching devices 74X in the OFF state to disconnect the impedancemodulating capacitors 63 from the receiving coil 51. In thisconfiguration, AC power induced in the receiving coil 51 is efficientlyoutput to the rectifying circuit 53 through the series capacitor 55.

In the switching device 74 of FIG. 8, since one side (source side) ofthe pair of switching devices 74X is essentially at ground, the circuitstructure of the control circuit 75 can be simplified. In particular,when the rectifying circuit 53 is a diode-bridge 53B, neither end of thereceiving coil 51 is at ground potential. Specifically, the receivingcoil 51 is connected to the ground line 78 through the diodes. In thiscase, the circuit structure of the control circuit 75 that controls thepair of switching devices 74X ON and OFF can be simplified.

Further, the device housing a battery 80 of FIG. 9 has a seriescapacitor 55 and impedance modulating capacitor 63 that are a singlecapacitor 86. In this device housing a battery 80, the switching device84 switches the capacitor 86 to use it as a series capacitor 55 or as animpedance modulating capacitor 63. The capacitor 86 is connected betweenthe receiving coil 51 and the rectifying circuit 53. The switchingdevice 84 is a shorting circuit 88 that short circuits the rectifyingcircuit 53 side of the capacitor 86. The shorting circuit 88 is made upof a resistance device 89 such as a positive temperature coefficient(PCT) thermistor and a switching device 84, and the switching device 84is controlled ON and OFF by a control circuit 85. The switching device84 is a phototransistor that is switched ON and OFF via light. When thecontrol circuit 85 switches the switching device 84 ON, the shortingcircuit 88 short circuits the rectifying circuit 53 side of thecapacitor 86 to connect the capacitor 86 in parallel with the receivingcoil 51. When the control circuit 85 switches the switching device 84OFF, the shorting circuit 88 is not short circuited but rather is opencircuited. This connects the capacitor 86 in series with the rectifyingcircuit 53 to output receiving coil 51 AC power to the rectifyingcircuit 53 through the capacitor 86.

As shown in FIGS. 1-7, the charging pad 10 is provided with atransmitting coil 11 connected to the AC power source 12 to induceelectromotive force (EMF) in the receiving coil 51, a case 20 housingthe transmitting coil 11 and having a top plate 21 to place a devicehousing a battery 50, a moving mechanism 13 housed in the case 20 tomove the transmitting coil 11 along the inside surface of the top plate21, and a position detection controller 14 that detects the position ofa device housing a battery 50 placed on the top plate 21 and controlsthe moving mechanism 13 to move the transmitting coil 11 close to thereceiving coil 51 of the device housing a battery 50. The transmittingcoil 11, AC power source 12, moving mechanism 13, and position detectioncontroller 14 are housed inside the case 20.

The charging pad 10 charges the battery 52 inside a device housing abattery 50 in the following manner.

(1) When a device housing a battery 50 is placed on the top plate 21 ofthe case 20, the position detection controller 14 detects its position.(2) The position detection controller 14, which has detected theposition of the device housing a battery 50, controls the movingmechanism 13 to move the transmitting coil 11 along the inside of thetop plate 21 and position it in close proximity to the receiving coil 51of the device housing a battery 50.(3) The transmitting coil 11, which has been moved close to thereceiving coil 51, is magnetically coupled to the receiving coil 51 andtransmits AC power to the receiving coil 51.(4) The device housing a battery 50 converts the receiving coil 51 ACpower to DC and charges the internal battery 52 with that DC power.

The charging pad 10, which charges the battery 52 in a device housing abattery 50 by the procedure described above, houses the transmittingcoil 11 connected to the AC power source 12 inside the case 20. Thetransmitting coil 11 is disposed beneath the top plate 21 of the case 20in a manner that allows it to move along the inside of the top plate 21.The efficiency of power transmission from the transmitting coil 11 tothe receiving coil 51 is improved by narrowing the gap between thetransmitting coil 11 and the receiving coil 51. With the transmittingcoil 11 moved into close proximity with the receiving coil 51, the gapbetween the transmitting coil 11 and the receiving coil 51 is preferablyless than or equal to 7 mm. Therefore, the transmitting coil 11 isdisposed under the top plate 21 and positioned as close as possible tothe top plate 21. Since the transmitting coil 11 is moved close to thereceiving coil 51 of a device housing a battery 50 placed on the topplate 21, the transmitting coil 11 is disposed in a manner that allowsit to move along the inside surface of the top plate 21.

The case 20 that houses the transmitting coil 11 is provided with aplanar top plate 21 where a device housing a battery 50 can be placed.The charging pad 10 of FIGS. 1 and 2 has an overall planar top plate 21that is disposed horizontally. The top plate 21 is made large enough toallow placement of devices housing a battery 50 having different sizesand shapes. For example, the top plate 21 can have a rectangular shapewith a side having a length of 5 cm to 30 cm. However, the top plate 21can also have a circular shape with a diameter of 5 cm to 30 cm. Thecharging pad 10 of FIGS. 1 and 2 has a large top plate 21 that allowssimultaneous placement of a plurality of devices housing a battery 50.Here, a plurality of devices housing a battery 50 is placed on the topplate 21 at the same time to allow sequential charging of their internalbatteries 52. Further, the top plate can also be provided withside-walls or other barriers around its perimeter, and devices housing abattery can be placed inside the side-walls to charge the internalbatteries.

The top plate 21 of the case 20 is translucent to allow visualconfirmation of the internal movement of the transmitting coil 11 fromthe outside. Since the user can visually confirm that the transmittingcoil 11 is in close proximity to the device housing a battery 50, theuser can dependably confirm charging of the device housing a battery 50.As a result, the user can operate the charging pad 10 with confidence.Further, light emitting diodes (LEDs) 19 can be provided to illuminatethe moving transmitting coil 11 and its vicinity. This can accentuatetransmitting coil 11 movement and create an aesthetically pleasingdesign. In addition, the LEDs 19 can be configured to shine through thetop plate 21 to illuminate the device housing a battery 50. The chargingpad 10 shown in FIGS. 2 and 3 has four LEDs 19 disposed at equalintervals around the transmitting coil 11. As shown in FIG. 7, theseLEDs 19 are energized by power supplied from a DC power supply 18 housedin the charging pad 10. However, LEDs can also be disposed at the centerregion of the transmitting coil. In addition, the number of LEDs used toshow the transmitting coil position can be three or less, or five ormore. With this charging pad 10, the device housing a battery 50 can beilluminated during charging, or visual effects such as the color orblinking pattern of the LEDs 19 can be changed depending on the state ofcharge. This type of charging pad 10 can clearly indicate to the userthe state of charge of a device housing a battery 50.

The transmitting coil 11 is wound in a plane parallel to the top plate21, and radiates AC magnetic flux above the top plate 21. Thistransmitting coil 11 emits AC magnetic flux perpendicular to, and beyondthe top plate 21. The transmitting coil 11 is supplied with AC powerfrom the AC power source 12 and radiates AC magnetic flux above the topplate 21. Wire can be wound around a magnetic material core 15 to make atransmitting coil 11 with high inductance. The core 15 is magneticmaterial with a high magnetic permeability such as ferrite and has theshape of an open end container. The core 15 has a solid circularcylinder 15A at the center of the spiral wound transmitting coil 11 anda circular cylindrical enclosure 15B around the outside that are joinedby a bottom section (refer to FIGS. 4 and 5). A transmitting coil 11with a core 15 can focus magnetic flux in a specific region toefficiently transmit power to the receiving coil 51. However, a magneticmaterial core is not always required in the transmitting coil, and acoil with no core can also be used. Since a coil with no core is light,the moving mechanism that moves the transmitting coil inside the topplate can be simplified. The transmitting coil 11 is made withessentially the same outside diameter as the receiving coil 51 toefficiently transmit power to the receiving coil 51.

The AC power source 12 supplies high frequency power, for example 20 kHzto several MHz, to the transmitting coil 11. The AC power source 12 isconnected to the transmitting coil 11 via flexible lead wires 16. Thisis because the transmitting coil 11 has to be moved close to the deviceshousing a battery 50 that are placed on the top plate 21. Although notillustrated, the AC power source 12 is provided with a self-excitedoscillator circuit, and a power amplifier to amplify the AC power outputfrom the self-excited oscillator circuit. The self-excited oscillatorcircuit uses the transmitting coil 11 as an oscillator circuit inductor.Consequently, the oscillator frequency changes with the inductance ofthe transmitting coil 11. The inductance of the transmitting coil 11changes with the relative position of the transmitting coil 11 withrespect to the receiving coil 51. This is because the mutual inductanceof the transmitting coil 11 and the receiving coil 51 changes with therelative position of the transmitting coil 11 with respect to thereceiving coil 51. Therefore, the frequency of the self-excitedoscillator circuit, which uses the transmitting coil 11 as an oscillatorcircuit inductor, changes as the transmitting coil 11 approaches thereceiving coil 51. As a result, the self-excited oscillator circuit candetect the relative position of the transmitting coil 11 with respect tothe receiving coil 51 from the change in oscillating frequency, and canbe used with the dual purpose as a position detection controller 14.

The transmitting coil 11 is moved in close proximity to the receivingcoil 51 by the moving mechanism 13. The moving mechanism 13 of FIGS. 2-5moves the transmitting coil 11 along the inside of the top plate 21 inthe X-axis and Y-axis directions to position it close to the receivingcoil 51. The moving mechanism 13 of the figures rotates threaded rods 23via servo motors 22 controlled by the position detection controller 14to move nut blocks 24 that are threaded onto the threaded rods 23. Thenut blocks 24 are moved to move the transmitting coil 11 close to thereceiving coil 51. The servo motors 22 are provided with an X-axis servomotor 22A to move the transmitting coil 11 in the X-axis direction, anda Y-axis servo motor 22B to move the transmitting coil 11 in the Y-axisdirection. The threaded rods 23 are provided with a pair of X-axisthreaded rods 23A to move the transmitting coil 11 in the X-axisdirection, and a Y-axis threaded rod 23B to move the transmitting coil11 in the Y-axis direction. The pair of X-axis threaded rods 23A aredisposed parallel to each other, and are connected via belts 25 torotate together when driven by the X-axis servo motor 22A. The threadednut blocks 24 are provided with a pair of X-axis nut blocks 24A that arethreaded onto each X-axis threaded rod 23A, and a Y-axis nut block 24Bthat is threaded onto the Y-axis threaded rod 23B. Both ends of theY-axis threaded rod 23B are connected to the X-axis nut blocks 24A in amanner allowing rotation. The transmitting coil 11 is mounted on theY-axis nut block 24B.

Further, the moving mechanism 13 of the figures has a guide rod 26disposed parallel to the Y-axis threaded rod 23B to move thetransmitting coil 11 in the Y-axis direction while retaining it in ahorizontal orientation. The guide rod 26 is connected at both ends tothe X-axis nut blocks 24A and moves together with the pair of X-axis nutblocks 24A. The guide rod 26 passes through a guide block 27 attached tothe transmitting coil 11 to allow transmitting coil 11 movement alongthe guide rod 26 in the Y-axis direction. Specifically, the transmittingcoil 11 is moved with horizontal orientation in the Y-axis direction viathe Y-axis nut block 24B and guide block 27 that move along the paralleldisposed Y-axis threaded rod 23B and guide rod 26.

When the X-axis servo motor 22A rotates the X-axis threaded rods 23A ofthis moving mechanism 13, the pair of X-axis nut blocks 24A move alongthe X-axis threaded rods 23A to move the Y-axis threaded rod 23B and theguide rod 26 in the X-axis direction. When the Y-axis servo motor 22Brotates the Y-axis threaded rod 23B, the Y-axis nut block 24B movesalong the Y-axis threaded rod 23B to move the transmitting coil 11 inthe Y-axis direction. Here, the guide block 27 attached to thetransmitting coil 11 moves along the guide rod 26 to maintain thetransmitting coil 11 in a horizontal orientation during movement in theY-axis direction. Consequently, rotation of the X-axis servo motor 22Aand Y-axis servo motor 22B can be controlled by the position detectioncontroller 14 to move the transmitting coil 11 in the X-axis and Y-axisdirections. However, the charging pad of the present invention is notlimited to a moving mechanism with the configuration described above.This is because any configuration of moving mechanism can be used thatcan move the transmitting coil in the X-axis and Y-axis directions.

Further, the charging pad of the present invention is not limited to amoving mechanism that moves the transmitting coil in the X-axis andY-axis directions. This is because the charging pad of the presentinvention can be provided with a straight-line guide wall on the topplate, the devices housing a battery can be aligned along the guidewall, and the transmitting coil can be moved in a straight-line alongthe guide wall. Although not illustrated, this charging pad can move thetransmitting coil in a straight-line along the guide wall with a movingmechanism that moves the transmitting coil in one direction such as inthe X-axis direction only.

The position detection controller 14 detects the position of a devicehousing a battery 50 that is placed on the top plate 21. The positiondetection controller 14 of FIGS. 2-5 detects the position of thereceiving coil 51 housed in the device housing a battery 50, and movesthe transmitting coil 11 close to the receiving coil 51. Further, theposition detection controller 14 is provided with a first positiondetection controller 14A that roughly determines the position of thereceiving coil 51, and a second position detection controller 14B thatdetermines the position of the receiving coil 51 with precision. In thisposition detection controller 14, the first position detectioncontroller 14A roughly determines the position of the receiving coil 51and controls the moving mechanism 13 to move the transmitting coil 11close to the receiving coil 51. Subsequently, the second positiondetection controller 14B detects the receiving coil 51 position withprecision while controlling the moving mechanism 13 to move thetransmitting coil 11 more accurately to the position of the receivingcoil 51. This charging pad 10 can quickly move the transmitting coil 11close to the receiving coil 51 with precision.

As shown in FIG. 6, the first position detection controller 14A isprovided with a plurality of position detection coils 30 fixed to theinside of the top plate 21, a detection signal generating circuit 31that supplies position detection signals to the position detection coils30, a receiving circuit 32 that receives echo signals from the positiondetection coils 30 resulting from excitation of the receiving coil 51 byposition detection signals supplied to the position detection coils 30from the detection signal generating circuit 31, and a discriminationcircuit 33 that determines receiving coil 51 position from the echosignals received by the receiving circuit 32.

The position detection coils 30 are made up of a plurality of coils inrows and columns. The plurality of position detection coils 30 is fixedwith specified intervals between each coil on the inside surface of thetop plate 21. The position detection coils 30 are provided with aplurality of X-axis detection coils 30A that detect receiving coil 51position on the X-axis, and a plurality of Y-axis detection coils 30Bthat detect receiving coil 51 position on the Y-axis. Each X-axisdetection coil 30A is a long narrow loop extending in the Y-axisdirection, and the X-axis detection coils 30A are fixed to the inside ofthe top plate 21 at specified intervals. The interval (d) betweenadjacent X-axis detection coils 30A is smaller than the outside diameter(D) of the receiving coil 51, and preferably the interval (d) betweenX-axis detection coils 30A is from 1 times to ¼ times the receiving coil51 outside diameter (D). The position of the receiving coil 51 on theX-axis can be detected more accurately by reducing the interval (d)between X-axis detection coils 30A. Each Y-axis detection coil 30B is along narrow loop extending in the X-axis direction, and the Y-axisdetection coils 30B are also fixed to the inside of the top plate 21 atspecified intervals. In the same manner as the X-axis detection coils30A, the interval (d) between adjacent Y-axis detection coils 30B issmaller than the outside diameter (D) of the receiving coil 51, andpreferably the interval (d) between Y-axis detection coils 30B is from 1times to ¼ times the receiving coil 51 outside diameter (D). Theposition of the receiving coil 51 on the Y-axis can also be detectedmore accurately by reducing the interval (d) between Y-axis detectioncoils 30B.

The detection signal generating circuit 31 issues pulse signals, whichare the position detection signals, with a specified timing. A positiondetection coil 30, which has input a position detection signal, excitesa nearby receiving coil 51 via the position detection signal. Thereceiving coil 51, which has been excited by a position detectionsignal, outputs an echo signal, which is generated by the energy of theinduced current flow, and that echo signal is detected by the positiondetection coil 30. Specifically, as shown in FIG. 10, following a givendelay time after a position detection signal has been input, thereceiving coil 51 generates an echo signal, and that echo signal isinduced in the position detection coil 30 near the receiving coil 51.The echo signal induced in the position detection coil 30 is sent fromthe receiving circuit 32 to the discrimination circuit 33. Thediscrimination circuit 33 uses the echo signal input from the receivingcircuit 32 to determine if the receiving coil 51 is close to theposition detection coil 30. When echo signals are induced in a pluralityof position detection coils 30, the discrimination circuit 33 determinesthat the position detection coil 30 with the largest amplitude echosignal is closest to the receiving coil 51.

The position detection controller 14 shown in FIG. 6 connects eachposition detection coil 30 to the receiving circuit 32 via a switchingmatrix 34. Since this position detection controller 14 can connect aplurality of position detection coils 30 by sequential switching, echosignals from a plurality of position detection coils 30 can be detectedwith one receiving circuit 32. However, a receiving circuit can also beconnected to each position detection coil to detect the echo signals.

In the position detection controller 14 of FIG. 6, the discriminationcircuit 33 controls the switching matrix 34 to sequentially switch eachof the position detection coils 30 for connection to the receivingcircuit 32. Since the detection signal generating circuit 31 isconnected outside the switching matrix 34, it outputs position detectionsignals to each position detection coil 30. The amplitude of theposition detection signals output from the detection signal generatingcircuit 31 to the position detection coils 30 is extremely largecompared to the echo signals from the receiving coil 51. The receivingcircuit 32 has a diode connected to its input-side that forms a voltagelimiting circuit 35. Position detection signals input to the receivingcircuit 32 from the detection signal generating circuit 31 are voltagelimited by the limiting circuit 35. Low amplitude echo signals are inputto the receiving circuit 32 without voltage limiting. The receivingcircuit 32 amplifies and outputs both position detection signals and theecho signals. An echo signal output from the receiving circuit 32 is asignal that is delayed from the position detection signal by a givendelay time such as several μsec to several hundred μsec. Since the echosignal delay time from the position detection signal is constant, asignal received after the constant delay time is assumed to be an echosignal, and the proximity of a position detection coil 30 to thereceiving coil 51 is determined from the amplitude of that echo signal.

The receiving circuit 32 is an amplifier that amplifies echo signalsinput from the position detection coils 30. The receiving circuit 32outputs each position detection signal and echo signal. Thediscrimination circuit 33 determines if the receiving coil 51 is placednext to a position detection coil 30 from the position detection signaland echo signal input from the receiving circuit 32. The discriminationcircuit 33 is provided with an analog-to-digital (A/D) converter 36 toconvert the signals input from the receiving circuit 32 to digitalsignals. Digital signals output from the A/D converter 36 are processedto detect the echo signals. The discrimination circuit 33 detects asignal that is delayed from the position detection signal by a givendelay time as an echo signal, and determines if the receiving coil 51 isclose to the position detection coil 30 from the amplitude of the echosignal.

The discrimination circuit 33 controls the switching matrix 34 tosequentially connect each of the plurality of X-axis detection coils 30Ato the receiving circuit 32 to detect the position of the receiving coil51 along the X-axis. For each X-axis detection coil 30A connected to thereceiving circuit 32, the discrimination circuit 33 outputs a positiondetection signal to that X-axis detection coil 30A and determines if thereceiving coil 51 is close to that X-axis detection coil 30A bydetection or lack of detection of an echo signal after a given delaytime from the position detection signal. The discrimination circuit 33connects each one of the X-axis detection coils 30A to the receivingcircuit 32, and determines if a receiving coil 51 is close to any of theX-axis detection coils 30A. If a receiving coil 51 is close to one ofthe X-axis detection coils 30A, an echo signal will be detected whenthat X-axis detection coil 30A is connected to the receiving circuit 32.Consequently, the discrimination circuit 33 can determine the positionof the receiving coil 51 along the X-axis from the X-axis detection coil30 that outputs an echo signal. When the receiving coil 51 straddles aplurality of X-axis detection coils 30, echo signals can be detected bya plurality of X-axis detection coils 30A. In that case, thediscrimination circuit 33 determines that the receiving coil 51 isclosest to the X-axis detection coil 30A that detects the strongest echosignal, which is the echo signal with the largest amplitude. Thediscrimination circuit 33 controls the Y-axis detection coils 30B in thesame manner to determine the position of the receiving coil 51 along theY-axis.

The discrimination circuit 33 controls the moving mechanism 13 accordingto the detected X-axis and Y-axis position to move the transmitting coil11 close to the receiving coil 51. The discrimination circuit 33controls the X-axis servo motor 22A to move the transmitting coil 11 tothe receiving coil 51 position on the X-axis. The discrimination circuit33 also controls the Y-axis servo motor 22B to move the transmittingcoil 11 to the receiving coil 51 position on the Y-axis.

The first position detection controller 14A moves the transmitting coil11 to a position close to the receiving coil 51 in the manner describedabove. The charging pad of the present invention can move thetransmitting coil 11 close to the receiving coil 51 with the firstposition detection controller 14A, and subsequently transmit power fromthe transmitting coil 11 to the receiving coil 51 to charge the battery52. However, the charging pad can further refine the position of thetransmitting coil 11 and move it still closer to the receiving coil 51to subsequently transmit power and charge the battery 52. Thetransmitting coil 11 is more precisely positioned close to the receivingcoil 51 by the second position detection controller 14B.

The second position detection controller 14B has an AC power source 12that is a self-excited oscillator circuit, and the second positiondetection controller 14B controls the moving mechanism 13 to move thetransmitting coil 11 to a position accurately determined by theoscillating frequency of the self-excited oscillator circuit. The secondposition detection controller 14B controls the moving mechanism 13X-axis servo motor 22A and Y-axis servo motor 22B to move thetransmitting coil 11 along the X and Y-axes while detecting the AC powersource 12 oscillating frequency. Self-excited oscillator circuitoscillating frequency characteristics are shown in FIG. 11. This figureshows the change in oscillating frequency as a function of the relativeoffset (displacement) between the transmitting coil 11 and the receivingcoil 51. As shown in this figure, the oscillating frequency of theself-excited oscillator circuit has a maximum where the transmittingcoil 11 and receiving coil 51 are closest, and the oscillating frequencydrops off as the two coils become separated. The second positiondetection controller 14B controls the moving mechanism 13 X-axis servomotor 22A to move the transmitting coil 11 along the X-axis, and stopsthe transmitting coil 11 where the oscillating frequency reaches amaximum. Similarly, the second position detection controller 14Bcontrols the Y-axis servo motor 22B in the same manner to move thetransmitting coil 11 along the Y-axis, and stops the transmitting coil11 where the oscillating frequency reaches a maximum. The secondposition detection controller 14B can move the transmitting coil 11 inthe manner described above to a position that is closest to thereceiving coil 51.

In the charging pad described above, the first position detectioncontroller 14A roughly detects the position of the receiving coil 51.Subsequently, the second position detection controller 14B finelyadjusts the transmitting coil 11 position to move it still closer to thereceiving coil 51. However, the position detection controller 44 shownin FIG. 12 and described below can move the transmitting coil 11 closeto the receiving coil 51 without fine adjustments.

As shown in FIG. 12, the position detection controller 44 is providedwith a plurality of position detection coils 30 fixed to the inside ofthe top plate, a detection signal generating circuit 31 that suppliesposition detection signals to the position detection coils 30, areceiving circuit 32 that receives echo signals from the positiondetection coils 30 resulting from excitation of the receiving coil 51 bypulse signals supplied to the position detection coils 30 from thedetection signal generating circuit 31, and a discrimination circuit 43that determines receiving coil 51 position from the echo signalsreceived by the receiving circuit 32. In this position detectioncontroller 44, the discrimination circuit 43 is provided with a memorycircuit 47 to store the amplitude of echo signals induced in eachposition detection coil 30 corresponding to receiving coil 51 position.Specifically, this is the amplitude of echo signals resulting fromreceiving coil 51 excitation that are induced in each position detectioncoil 30 after a given delay time, as shown in FIG. 10. The positiondetection controller 44 detects the amplitude of the echo signal inducedin each position detection coil 30, and compares the detected echosignal amplitude with the echo signal amplitudes stored in the memorycircuit 47 to determine the receiving coil 51 position.

The position detection controller 44 determines receiving coil 51position from the amplitude of the echo signal induced in each positiondetection coil 30 in the following manner. The position detection coils30 shown in FIG. 12 are provided with a plurality of X-axis detectioncoils 30A that detect receiving coil 51 position on the X-axis, and aplurality of Y-axis detection coils 30B that detect receiving coil 51position on the Y-axis. The position detection coils 30 are fixed to theinside of the top plate 21 at specified intervals. Each X-axis detectioncoil 30A is a long narrow loop extending in the Y-axis direction, andeach Y-axis detection coil 30B is a long narrow loop extending in theX-axis direction. FIG. 13 shows the amplitude of the echo signal inducedin each X-axis detection coil 30A as the receiving coil 51 is movedalong the X-axis. The horizontal axis of FIG. 13 shows the position ofthe receiving coil 51 on the X-axis, and the vertical axis shows theamplitude of the echo signal induced in each X-axis detection coil 30A.This position detection controller 44 can determine the position of thereceiving coil 51 on the X-axis by detecting the amplitude of the echosignal induced in each X-axis detection coil 30A. As shown in FIG. 13,the amplitude of the echo signal induced in each X-axis detection coil30A changes as the receiving coil 51 position along the X-axis changes.For example, when the center of the receiving coil 51 is at the centerof the first X-axis detection coil 30A, the amplitude of the echo signalinduced in the first X-axis detection coil 30A is a maximum as shown bypoint A in FIG. 13. When the receiving coil 51 is halfway between thefirst and second X-axis detection coils 30A, the amplitude of the echosignals induced in the first and second X-axis detection coils 30A isequal as shown by point B in FIG. 13. Specifically, the amplitude of anecho signal detected in an X-axis detection coil 30A is maximum(strongest signal) when the receiving coil 51 is closest to thatdetection coil, and the amplitude of the echo signal decreases as thereceiving coil 51 is separated from that detection coil. Therefore, theX-axis detection coil 30A closest to the receiving coil 51 can bedetermined by which X-axis detection coil 30A has the largest amplitudeecho signal. When echo signals are induced in two X-axis detection coils30A, the direction of receiving coil 51 offset from the X-axis detectioncoil 30A with the largest echo signal amplitude can be determined fromthe direction, relative to the X-axis detection coil 30A with thelargest echo signal, of the other X-axis detection coil 30A that detectsan echo signal. Further, the relative position of the receiving coil 51between two X-axis detection coils 30A can be determined from the ratioof the amplitudes of the echo signals induced in the two X-axisdetection coils 30A. For example, if the ratio between echo signalamplitudes detected in two X-axis detection coils 30A is one, thereceiving coil 51 position can be determined to be halfway between thetwo X-axis detection coils 30A.

The discrimination circuit 43 stores in the memory circuit 47 the echosignal amplitude induced in each X-axis detection coil 30A correspondingto receiving coil 51 position on the X-axis. When a receiving coil 51 isplaced on the charging pad 10, an echo signal is detected in one of theX-axis detection coils 30A. Therefore, the discrimination circuit 43 candetermine from the echo signal induced in the X-axis detection coil 30Athat a receiving coil 51 has been placed on the charging pad 10; namely,that a device housing a battery 50 has been placed on the charging pad10. Further, by comparing the amplitude of the echo signal induced ineach X-axis detection coil 30A with the amplitudes stored in the memorycircuit 47, the position of the receiving coil 51 on the X-axis can bedetermined. The discrimination circuit can also store a function in thememory circuit that specifies receiving coil X-axis positioncorresponding to the ratio of the amplitudes of echo signals induced inadjacent X-axis detection coils. Receiving coil position can bedetermined from the function stored in memory. This function can bedetermined by moving the receiving coil between two X-axis detectioncoils and measuring the ratio of the echo signal amplitudes in the twodetection coils. Here, the discrimination circuit 43 detects the ratioof the amplitudes of echo signals induced in two X-axis detection coils30A. Based on the function stored in memory, the X-axis position of thereceiving coil 51 between the two X-axis detection coils 30A can becomputed from the detected echo signal amplitude ratio.

Discrimination circuit 43 detection of receiving coil 51 X-axis positionfrom echo signals induced in the X-axis detection coils 30A is describedabove. Receiving coil 51 position on the Y-axis can be detected in asimilar manner from echo signals induced in the Y-axis detection coils30B.

When the discrimination circuit 43 has detected the receiving coil 51position on the X and Y-axes, the position detection controller 44 movesthe transmitting coil 11 to the receiving coil 51 position based on aposition signal issued from the discrimination circuit 43.

When an echo signal is detected having a waveform as describedpreviously, the charging pad discrimination circuit 43 can recognize anddistinguish that a receiving coil 51 of a device housing a battery 50has been placed on the charging pad. When a waveform is detected anddetermined to be different from an echo signal, an object other than thereceiving coil 51 of a device housing a battery 50 (for example, a metalforeign object) is assumed to be on the charging pad and the supply ofpower can be terminated. In addition, when no echo signal waveform isdetected, it is assumed that no device housing a battery 50 receivingcoil 51 has been placed on the charging pad and power is not supplied.

The charging pad 10 position detection controller 14, 44 controls themoving mechanism 13 to move the transmitting coil 11 close to thereceiving coil 51. In this state, AC power is supplied to thetransmitting coil 11 from the AC power source 12. AC power from thetransmitting coil 11 is transmitted to the receiving coil 51 and used tocharge the battery 52. The position detection controller 14 shown inFIG. 7 houses a detection circuit 17 that detects battery informationsent from the device housing a battery 50. The detection circuit 17controls battery 52 charging voltage and current to charge the battery52 based on the battery information sent from the device housing abattery 50. Full-charge of the battery 52 is transmitted as battery datafrom the device housing a battery 50. Consequently, the detectioncircuit 17 detects full-charge of the battery 52 from the batteryinformation sent from the device housing a battery 50 and stops thesupply of AC power to the transmitting coil 11 to terminate charging.

A charging pad 10, which has a top plate 21 where a plurality of deviceshousing a battery 50 can be placed, sequentially charges the battery 52in each device housing a battery 50 to full-charge. As shown in FIG. 1,the charging pad 10 first detects the position of the receiving coil 51in any one of the devices housing a battery 50 (the first device housinga battery 50A). The transmitting coil 11 is moved close to the receivingcoil 51, and the battery 52 in the first device housing a battery 50A ischarged to full-charge. When the battery 52 in the first device housinga battery 50A reaches full-charge and the detection circuit 17 receivesa full-charge signal from that device housing a battery 50A, theposition detection controller 14 detects the position of anotherreceiving coil 51 in a second device housing a battery 50B and controlsthe moving mechanism 13 to move the transmitting coil 11 to thereceiving coil 51 of the second device housing a battery 50B. In thisstate, power is transmitted to charge the battery 52 in the seconddevice housing a battery 50B and that battery 52 is charged tofull-charge. When the battery 52 in the second device housing a battery50B reaches full-charge and the detection circuit 17 receives afull-charge signal transmitted from the second device housing a battery50B, the position detection controller 14 detects the position of thereceiving coil 51 in a third device housing a battery 50C and controlsthe moving mechanism 13 to move the transmitting coil 11 to thereceiving coil 51 of the third device housing a battery 50C. In thisstate, power is transmitted to charge the battery 52 in the third devicehousing a battery 50C and that battery 52 is charged to full-charge. Inthis manner, when a plurality of devices housing a battery 50 are placedon the top plate 21, the charging pad 10 sequentially switches from onedevice housing a battery 50 to another to fully charge all the internalbatteries 52. This charging pad 10 stores in memory the location ofdevices housing a battery 50 that have been fully charged, and does notcharge the batteries 52 in devices that have been fully charged. Whenfull-charge of the batteries 52 in all the devices housing a battery 50placed on the top plate 21 has been detected, the charging pad 10suspends operation of the AC power source 12 and stops battery 52charging. In the embodiments described above and below, charging of thebattery 52 in a device housing a battery 50 is stopped when full-chargeis reached. However, it is also possible to treat a specific batterycapacity as full-charge and stop charging when that specific batterycapacity is reached.

As described above, a charging pad 10 that fully charges batteries 52 ina plurality of devices housing a battery 50 can move the transmittingcoil 11 to the receiving coil 51 of the next device housing a battery 50to fully charge the battery 52 in the next device when the battery 52 inthe previous device has been fully charged. This can sequentially chargethe batteries 52 in a plurality of devices housing a battery 50 tofull-charge. Further, a charging pad 10 that charges a plurality ofdevices housing a battery 50 can move the transmitting coil 11 to thereceiving coil 51 of another device housing a battery 50 when thebattery 52 in the device housing a battery 50 presently being chargedhas not reached full-charge. By repeating this procedure, namely byswitching one after another the device housing a battery 50 that isbeing charged, the battery 52 in each device housing a battery 50 can befully charged. For example, the charging pad 10 detection circuit 17 candetect battery data such as battery voltage, remaining capacity, andbattery temperature transmitted from the device housing a battery 50being charged, and switch the device housing a battery 50 based on thedetected data. The charging pad 10 can also move the transmitting coilto the receiving coil of another device housing a battery to switch thedevice housing a battery being charged when a specified time haselapsed. A charging pad that switches the device housing a battery beingcharged based on battery voltage switches the device when batteryvoltage reaches a predetermined voltage or when the rate of rise involtage of the battery being charged becomes equal to a set value. Thecharging pad can detect remaining battery capacity to switch the devicehousing a battery being charged. Here, the device housing a batterybeing charged is switched when the remaining capacity of the batterybeing charged reaches a set capacity or when the change in remainingcapacity becomes equal to a set value. The charging pad can detectbattery temperature to switch the device housing a battery beingcharged. Here, the device housing a battery being charged is switchedwhen the temperature of the battery being charged reaches a settemperature. A charging pad that switches the device housing a batterybeing charged when a set time has elapsed houses a timer, and the devicehousing a battery being charged is switched when the timer times out. Inaddition, the charging pad can also switch the device housing a batterybeing charged based on all the battery data including voltage, remainingcapacity, temperature, and charging time.

The charging pad 10 described above charges the battery 52 in the nextdevice housing a battery 50 before the previous battery 52 has reachedfull-charge. Since the charging pad 10 repeats this procedure to chargethe devices housing a battery 50, the power transmitted from thetransmitting coil 11 to the receiving coil 51 can be increased to fullycharge a plurality of devices housing a battery 50 in a short timeperiod. This is because battery 52 charging current can be increasedwhen charging a single battery 52 for only a short time period. Thepower transmitted by a charging pad, which transmits power in anon-contact manner from a transmitting coil 11 to a receiving coil 51 inclose proximity, is limited by unavoidable receiving coil and batteryheat generation caused by magnetic flux leakage. However, by switchingthe device housing a battery 50 during charging, the transmitted powercan be increased while preventing receiving coil 51 and battery 52 heatgeneration. Specifically, battery 52 charging current can be increasedto rapidly charge the battery 52 to full-charge. This is because thebattery 52 and receiving coil 51 are cooled during the periods whencharging is not being performed. Consequently, a charging pad 10, whichswitches the device housing a battery 50 being charged prior to reachingfull-charge, has the characteristic that the batteries 52 can be rapidlycharged to full-charge while limiting receiving coil 51 and battery 52heating.

As shown for example in FIG. 1, where three devices housing a battery 50are placed on the top plate 21, the battery 52 in each device housing abattery 50 can be charged to full-charge in the following manner.

(1) First, the position of the receiving coil 51 in any one of thedevices housing a battery 50 is detected, and the transmitting coil 11is moved close to the receiving coil 51 to charge the battery 52 in thefirst device housing a battery 50A.(2) The position detection controller 14 suspends charging of thebattery 52 in the first device housing a battery 50A based on data suchas battery voltage, remaining battery capacity, and battery temperaturetransmitted from the first device housing a battery 50A. The position ofthe receiving coil 51 in the second device housing a battery 50B, whichis placed in a different location from the first device housing abattery 50A, is detected. The moving mechanism 13 is controlled to movethe transmitting coil 11 close to the receiving coil 51 in the seconddevice housing a battery 50B. In this state, power is transmitted to thesecond device housing a battery 50B to charge that battery 52.(3) The position detection controller 14 suspends charging of thebattery 52 in the second device housing a battery 50B based on batterydata transmitted from the second device housing a battery 50B. Theposition of the receiving coil 51 in the third device housing a battery50C, which is placed in still a different location, is detected. Themoving mechanism 13 is controlled to move the transmitting coil 11 closeto the receiving coil 51 in the third device housing a battery 50B tocharge the battery 52 in the third device housing a battery 50B.(4) Next, The position detection controller 14 suspends charging of thebattery 52 in the third device housing a battery 50C based on batterydata transmitted from the third device housing a battery 50C, and thetransmitting coil 11 is moved to the position of the receiving coil 51in the first device housing a battery 50A to charge the battery 52 inthat device.(5) In the manner described above, the first device housing a battery50A, the second device housing a battery 50B, and the third devicehousing a battery 50C are repeatedly charged to charge their internalbatteries 52 to full-charge. During the process of battery 52 chargingwhile switching the devices housing a battery 50, if any one of thebatteries 52 becomes fully charged, charging is terminated for thatdevice housing a battery 50 and the batteries 52 of the next deviceshousing a battery 50 are sequentially charged to full-charge. Whenfull-charge is detected for the batteries 52 in all the devices housinga battery 50 placed on the top plate 21, the charging pad 10 stopsoperation of the AC power source 12 and terminates battery 52 charging.

It should be apparent to those with an ordinary skill in the art thatwhile various preferred embodiments of the invention have been shown anddescribed, it is contemplated that the invention is not limited to theparticular embodiments disclosed, which are deemed to be merelyillustrative of the inventive concepts and should not be interpreted aslimiting the scope of the invention, and which are suitable for allmodifications and changes falling within the spirit and scope of theinvention as defined in the appended claims.

The present application is based on Application No. 2009-142793 filed inJapan on Jun. 15, 2009, the content of which is incorporated herein byreference.

What is claimed is:
 1. A battery housing device comprising: an internalbattery housed in the battery housing device; and a receiving coil thatsupplies charging power to the internal battery by magnetically couplingwith a transmitting coil of a charging pad, wherein the battery housingdevice further comprises a modulator circuit that modulates an impedanceof the receiving coil with a digital signal, wherein the modulatorcircuit comprises: a load circuit connected in parallel with thereceiving coil, the load circuit having a switching device connected inseries with an impedance modulating capacitor; and a control circuitthat switches the switching device of the load circuit ON and OFF inaccordance with the digital signal.
 2. The battery housing device ascited in claim 1, wherein the load circuit further comprises a pair ofseries-connected switching devices, and an impedance modulatingcapacitor connected in series with each of the switching devices;wherein a connection node between the pair of switching devices isconnected to a ground line, and the pair of switching devices issimultaneously controlled ON and OFF by the control circuit.
 3. Thebattery housing device as cited in claim 1, wherein the digital signalthat the battery housing device transmits to the charging pad is relatedto battery information of the internal battery.
 4. The battery housingdevice as cited in claim 3, wherein the battery information of theinternal battery comprises at least one battery information elected frombattery voltage during charging, battery charging current, batterytemperature, a serial number of the battery, allowable charging currentthat sets the charging current for the battery, allowable batterytemperature that controls battery charging, remaining capacity andfull-charge of the battery.
 5. The battery housing device as cited inclaim 1, wherein the battery housing device is a battery pack or amobile telephone.
 6. A circuit of a battery housing device comprising: amodulator circuit that modulates an impedance of a receiving coil of thebattery housing device with a digital signal, the receiving coilsupplying charging power to an internal battery of the battery housingdevice by magnetically coupling with a transmitting coil of a chargingpad, wherein the modulator circuit comprises: a load circuit connectedin parallel with the receiving coil, the load circuit having a switchingdevice connected in series with an impedance modulating capacitor; and acontrol circuit that switches the switching device of the load circuitON and OFF in accordance with the digital signal.
 7. The circuit ascited in claim 6, further comprising a receiving coil that suppliescharging power to an internal battery of the battery housing device bymagnetically coupling with a transmitting coil of a charging pad.
 8. Thecircuit as cited in claim 6, wherein the load circuit further comprisesa pair of series-connected switching devices, and an impedancemodulating capacitor connected in series with each of the switchingdevices; wherein a connection node between the pair of switching devicesis connected to a ground line, and the pair of switching devices issimultaneously controlled ON and OFF by the control circuit.
 9. Thecircuit as cited in claim 6, wherein the digital signal is related tobattery information of the internal battery.
 10. The circuit as cited inclaim 9, wherein the battery information of the internal batterycomprises at least one battery information elected from battery voltageduring charging, battery charging current, battery temperature, a serialnumber of the battery, allowable charging current that sets the chargingcurrent for the battery, allowable battery temperature that controlsbattery charging, remaining capacity and full-charge of the battery. 11.A circuit of a battery housing device comprising: a control circuit thatcontrols a modulator circuit to modulate an impedance of a receivingcoil of the battery housing device with digital signal, the receivingcoil supplying charging power to an internal battery of the batteryhousing device by magnetically coupling with a transmitting coil of acharging pad, wherein the control circuit switches a switching device ofa load circuit ON and OFF in accordance with the digital signal, theload circuit being connected in parallel with the receiving coil, andthe switching device of the load circuit being connected in series withan impedance modulating capacitor.
 12. The circuit as cited in claim 11,wherein the load circuit comprises a pair of series-connected switchingdevices, and an impedance modulating capacitor connected in series witheach switching device, wherein the connection node between the pair ofswitching devices is connected to the ground line, and wherein the pairof switching devices is simultaneously controlled ON and OFF by thecontrol circuit.
 13. The circuit as cited in claim 11, wherein thedigital signal is related to battery information of the internalbattery.
 14. The circuit as cited in claim 13, wherein the batteryinformation of the internal battery comprises at least one batteryinformation elected from battery voltage during charging, batterycharging current, battery temperature, a serial number of the battery,allowable charging current that sets the charging current for thebattery, allowable battery temperature that controls battery charging,remaining capacity and full-charge of the battery.
 15. The batteryhousing device as cited in claim 3, wherein the battery housing devicefurther comprises a battery data detection circuit that detects thebattery information of the internal battery, the battery data detectioncircuit being connected between the internal battery and the modulatorcircuit.